1. Field of the Invention
The present invention relates to an image forming apparatus including an air cleaner.
2. Description of Related Art
Common image forming apparatuses include an air cleaner for expelling air inside the apparatus to the outside. More specifically, in a fixing unit of the image forming apparatus, emissions such as an odor, volatile organic compounds (VOC), low molecular siloxane, dust (toners or paper dust), etc., are produced. The air cleaner includes a ventilator (typically, a fan) and a filter in an air passage. The ventilator is driven to collect air around the fixing unit. Emissions contained in the collected air are captured by the filter, and the cleaned air is expelled to the outside of the apparatus. Also, the image forming apparatus includes another ventilator for cooling a developing unit or paper sheets. An air flow produced by this ventilator is also expelled to the outside of the apparatus via the air cleaner.
In recent years, concern about the air quality has been increasing, and hence, there has been a demand for an image forming apparatus which is capable of cleaning air of an installation space.
In view of the above background, image forming apparatuses which are capable of cleaning air inside and outside the apparatuses have been recently proposed. For example, Japanese Patent Laid-Open Publication No. 2012-203251 discloses the following image forming apparatus. Specifically, an inside-air duct takes in the air inside the apparatus, and an outside-air duct takes in the air of the installation space of the apparatus (i.e., the air outside the apparatus). These air flows are merged and guided through a common duct and passed through an exhaust gas filter placed in the common duct. Thereafter, the air which has been passed through the exhaust gas filter is expelled to the outside of the apparatus from a common outlet placed at the most downstream position of the common duct.
However, in the case where the air from the inside and outside of the apparatus are expelled from the common outlet as in Japanese Patent Laid-Open Publication No. 2012-203251, a backflow is likely to occur due to interaction between the inside-air duct and the outside-air duct. This is because, when the flow rate in the inside-air duct varies, the pressure at the junction of the inside-air duct and the outside-air duct varies, and the pressure variation affects the flow rate in the outside-air duct. Particularly, there is a probability that emissions are remaining in the air inside the apparatus, and therefore, it is necessary to avoid a backflow to the outside-air duct when the flow rate in the inside-air duct varies.
Thus, an object of the present invention is to provide an image forming apparatus which is capable of preventing a backflow of air from the inside-air duct to the outside-air duct.